Experimental measurement of leakage flow in centrifugal blood pump

• Main Author: Ong, Li Xuan.
• Other Authors: Wong Yew Wah
• Format: Final Year Project
• Language: English
• Published: 2009
• Subjects: DRNTU::Engineering::Mechanical engineering::Fluid mechanics
• Online Access: http://hdl.handle.net/10356/16822
• Institution: Nanyang Technological University

In the design of a blood pump, leakage flow study is crucial as high leakage flow is necessary for good washout within the pump, thereby preventing thrombus formation. However, excessive leakage flow will lead to hemolysis due to high fluid shear stress. Therefore, there is a need to determine the optimized clearance gap size. Initially, investigation and adjustment of the experiment test rig was conducted to improve the reliability of the instrument. Experiments were carried out at four gap sizes and two rotational speeds to establish the pump characteristics, to measure the pressure difference between the outer and inner radii of the impeller, and the leakage flow rate in the clearance gap. To conduct leakage flow measurements and to ensure better accuracy of the results, annular strips of shims were added onto the volute interior surface to prevent the flow from flowing directly into the impeller eye. The experimental results showed that the pump performance at a gap size of 0.17mm is not significant due to high frictional torque generated at smallest clearance gap. A proposed explanation for the high frictional torque was the high mean pressure measured at 0.17mm gap due to high resistance of the flow. The leakage flow measurement results showed that throttling, varying pump speeds and clearance gap size have a direct effect on the measurement. At low operating flow rate, higher rotational speed and larger gap size yield a higher leakage flow rate. A linear relationship between mean pressure and leakage flow was found when the graph of mean pressure against leakage flow rate was plotted. A comparison between experimental results with theoretical and CFX results shows high accuracy of the measurements taken at 0.17mm gap. In general, experimental results yield a lower measurement of leakage flow rate, and a proposed interpretation of this result is the limited tapping points on the volute used to measure the accurate amount of leakage flow in the gap region.